Village afforestation must meet the needs of farmers for
quick tangible returns. The growth of food crops among trees
appears to be a promising incentive. Research to ascertain
appropriate species and mixtures, and appropriate espacements and
rotations to maximize production, are described.

Good food crop yields are obtained in the first year of
intercropping but fall off in the second and subsequent years
with trees at close espacement. Wider tree espacement is likely
to prolong useful food cropping. Trees intercropped with food
crops show growth as good, or nearly as good, as trees grown
under clean-weeded conditions and much superior growth to trees
raised under spot-weeded or unweeded conditions

It is recommended that similar trials be established for
various tree and food crops over a range of ecological sites.
These will serve also as valuable demonstration plots.

Introduction

King and Chandler (1978) emphasize that the term agro-forestry
may be applied to a wide spectrum of land-use combinations. These
range from taungya (or agrisilviculture) to the selective use of
trees as shelterbelts in a predominantly agricultural system.

Many traditional farming systems already include the permanent
cultivation of a balanced mixture of tree species and
agricultural crops. The trees often provide an immediate economic
return in terms of direct products in addition to the indirect
benefits of improving the ecological conditions for the food
crops and animals.

Examples in high rainfall areas are the integrated farming
systems developed in Latin America, where Cordia alliodora and
Cedrela odorata are grown over lemon, bananas, and plantains,
which are in turn underplanted with coffee, or the Kandy spice
gardens of Sri Lanka, where tree crops such as nutmeg, cloves,
and jackfruit are underplanted with coffee, bananas, pepper, and
vegetables (cf. the paper by Watson in this volume, pp. 6-12). In
Africa a good example is the land use on the slopes of Mount
Kilimanjaro, where coffee, bananas, and annual food crops are
intermixed with timber trees such as Grevillea robusta.

Trees have also been combined with a more limited agricultural
cropping programme. For example, the taungya system was designed
primarily for the establishment of permanent timber crops. It was
most successful in areas where there was a shortage of good
agricultural land. King (1968) expresses concern that the peasant
labour involved is exploited because the forest services benefit
from their efforts and pay no remuneration. However, it is
noteworthy that despite dilution with the tree crop, per hectare
yields to the farmers are higher than on land available to them
outside the reserves. In fact, Hofstad (1978) has calculated that
in north-eastern Tanzania the value of the food crops grown under
the taungya system may far outweigh the discounted value of the
subsequent tree crops.

Peasant farmers in all countries are naturally conservative:
change usually involves risk, and they are unwilling to undertake
change without convincing evidence of guaranteed personal
financial or material advantages. They have very limited capital
reserves to sustain them; thus, change should provide immediate,
or short-term, returns. Furthermore, peasant farmers belong to
closely integrated communities that are economically
interdependent. Suggested changes should benefit the whole
community and cause minimal disruption to existing social
structures and customary practices.

The "felt needs" of a rural community are for a
sustainable system of land management that will produce
acceptable food for people and animals, maintain fertility and
water balance, and provide a renewable source of firewood and
building poles within walking distance of the village. A
successful agro-forestry system for a farming community must meet
specific needs in these areas, must provide obvious short-term
personal advantages for the farmer, and, as far as possible,
should be consistent with local traditional working habits and
patterns of family labour,

Intercropping of selected tree species and agricultural crops
may be competitive or collaborative. Traditional systems have
developed over time to select effective mixtures; development of
new systems will require research into many factors, including
appropriate species and mixtures, and appropriate spacings and
rotations to maximize production.

The Division of Forestry at Morogoro, Tanzania, is currently
initiating research to assess the effects and productivity of
intercropping selected tree species with staple food crops over
an extended period.

Agro-forestry Research at Morogoro, Tanzania

The rainfall at Morogoro is about 800 mm a year, falling
mainly between March and May, but sometimes with a substantial
amount in November. Unfortunately for the farmer it is very
unpredictable in its regularity. Although Morogoro does not lie
within the humid tropics, the research being carried out is of
wider application. The investigations are simple in design, the
field work is easy to carry out and applicable over a wide range
of ecological conditions. Very important also, this type of trial
gives quick interim results that can be easily seen and
understood.

Trials of Eucalyptus melliodora with Different Crops

The layout of the trial and early results have been previously
described by Maghembe and Redhead (1981). Containergrown
Eucalyptus melliodora were planted in February 1978 in farmland
that had been ploughed and harrowed. The tree seedlings were
planted at a spacing of 2.5 x 2.5 m and intercropped with maize,
sorghum, and beans, which were planted at 90 x 30 cm, 60 x 15 cm,
and 40 x 20 cm, respectively. The same three crops were planted
again in 1979 and 1980. Yields of maize and beans were recorded;
sorghum was not harvested as the crop was eaten by birds. Both
weed-free and unweeded plots of E melliodora were also grown as
controls. No fertilizers were used, and the experiment was
arranged as a latin square. Each plot contained 5 x 5 trees, and
the central core of 3 x 3 trees was periodically measured. The
area was clear-felled in March 1981, and the leaf litter and
standing biomass assessed. The same food crops were sown again so
that yields along with coppice could be ascertained.

The yield of maize was 1,280 kg/ha in the first year and 100
kg/ha in the second year. In the third year it did not flower.
Sorghum followed a similar pattern, although yields were not
recorded. At 2.5 x 2.5 m spacings, the trees were too close to
permit sufficient light for maize and sorghum to grow after the
first year. The yields of beans for the three years were poor; in
the first year, when good yields were expected, the crop was
badly attacked by an unidentified fungus. In the second year the
beans appeared healthy but the yield was only 150 kg/ha. In the
third year the beans were etiolated and the yield was
insignificant. At the time of the first harvest, the mean height
of the Eucalyptus in unweeded plots was significantly lower than
Eucalyptus in intercropped or weed-free treatments, in which
heights did not differ significantly. The trees in the beans and
clean-weeded plots were noticeably more robust and more heavily
branched than the trees among maize and sorghum, which were
spindly due to competition for light (figs. 1-2). Survival of the
trees has been approximately 90 per cent, except in the unweeded
plots, where half died during the first two years.

At three years of age, the stand has yielded more than 1,000
poles/ha suitable for house building and more than 6 m³ /ha of
fuelwood. The mean size of trees grown among beans is not
significantly different from that of those grown in weed-free
plots, and the trees intercropped with maize and sorghum are
two-thirds the size of clean-weeded trees. The maize and sorghum
yield would clearly make up in value for the reduced volume of
the tree crop.

It was apparent from this trial that normal yields of
agricultural crops could be expected in the first year with
little effect on the tree crop in the case of Eucalyptus
melliodora, but for food production in subsequent years wider
spacing of the trees is necessary.

Trials of Trees at Different Spacings with Crops

It was primarily to determine how far apart the trees could be
and still produce an acceptable volume of firewood or
appropriately shaped poles that a series of more elaborate
long-term investigations was laid down in 1980. Another objective
was to test tree species that would provide both fuel and fodder.
Four trials were established: (1) Eucalyptus camaldulensis
(planted for fuel and pole production) with maize and beans; (2)
Acacia albida (planted for fodder and fuel production) with maize
and beans; (3) Leucaena leucocephala (planted for fuel
production) with maize and beans; (4) Leucaena leucocephala
(planted for fodder production) with maize and beans.

The layout of these investigations has been described by
Maghembe and Redhead (1981). Briefly, tree seedlings were
container-grown and planted in ploughed and harrowed land. Each
investigation has a split-plot layout with food crops (maize or
beans) and weeding treatments (spot-weeded or clean-weeded)
forming the main plots, and tree spacings forming the sub-plots.
The maize was planted at 75 cm x 30 cm, leaving a circle of 50 cm
radius around each tree; fertilizer was applied at a rate of 400
kg/ha ammonium sulphate and 200 kg/ha triple superphosphate, in
two applications. The beans were planted at 40 cm x 20 cm,
leaving a circle of 20 cm radius around each tree seedling;
fertilizer was applied at a rate of 200 kg/ha ammonium sulphate
and 200 kg/ha triple ammonium phosphate, with the former applied
when the beans were well established. Clean weeding was done by
harrow, supplemented by hoeing; no fertilizer was applied in
these plots. Spotweeding was done by hoe in a circle of 50 cm
radius around each tree, as in normal Tanzanian forestry
practice; no fertilizer was applied. This main-plot treatment was
omitted from trials 2 and 4.

With regard to the spacing, trials 1 and 3 had sub-plots with
trees at 3 x 3 m, 4 x 4 m, and 5 x 5 m, respectively. In trial 2,
the 3 x 3 m spacing was replaced by a 6 x 6 m spacing in order to
maximize fodder production. Similarly, in trial 4, the Leucaena
leucocephala was planted in rows 3, 4, 5, and 6 m apart to
maximize fodder production. Trees within rows were only one metre
apart. In all four trials sub-plots without trees were planted as
controls.

Long term soil studies are in progress so that soil under
Eucalyptus, Acacia, and Leucaena can be compared with soil under
fallow and under pure food crops. The nitrogenfixing activity of
the Acacia and Leucaena is being measured with a portable
gas-liquid chromatograph.

The trees in all investigations were too young to have had a
marked effect on the maize and bean yields during the first
cropping season apart from the space they occupied. Differences
are expected to show up from the second year onwards, when the
canopy starts to close. Unfortunately, the yield of maize and
beans was normal in only one set of plots combining Leucaena. In
this case, the mean yield of maize was 1,645 kg/ha, which
compares favourably with yields obtained on the university farm
and is over twice the national average in Tanzania of 670 kg/ha
(Acland 1971). The mean yield of beans was 401 kg/ha, an average
yield by peasant standards (Acland 1971).

In the other investigations the planting time and tasselling
time of maize coincided with a severe drought, and growth yields
were very poor and uneven. The drought caused great variation in
the interaction between the food and tree crops and masked the
significance of the results.

In contrast with the little effect the trees had on the food
crops, the maize in particular has had a marked effect on the
trees because it is a tall crop casting considerable shade (figs.
3-6). In all investigations, at the time of maize harvest, the
trees among maize were taller than those in other treatments-24
per cent taller in both stands of Leucaena and 20 per cent taller
in the Eucalyptus The height differences were statistically
highly significant except in the Acacia plots, where the
maize-grown trees were only 13 per cent taller. After harvest,
the clean-weeded trees grew best, and in all cases their height
surpassed that of trees in other treatments by the end of the
year. The spot-weeded treatment has proved much inferior to the
other treatments, as the trees are only two-thirds of the height
of clean-weeded trees and approximately 20 per cent less in
height than trees intercropped with either maize or beans. These
growth trends are emphasized even more by the differences in
root-collar diameter (fig. 7).

The results demonstrate that good food yields can be obtained,
at least during the first year of intercropping with trees. The
trees benefit more from the weeding associated with growing food
crops than they do from the Tanzanian standard practice of spot
weeding. Moreover, spot weeding allows a dense growth of grass to
grow in the intervening spaces, and this is a serious fire
hazard. Clean weeding gives the best growth, but it is not
realistic to expect this in community afforestation projects.

It will be interesting to monitor the subsequent yields of
food crops at the wider tree spacings. If a valuable pole and
fuel crop is nearing harvest by the time food yields drop
seriously, agro-forestry in this form could become a standard
practice in community afforestation projects. Should tree
intercropping prove beneficial in improving soil fertility, this
will have great significance for areas where a shortage of land
precludes a long natural fallow.

It is suggested that trials of similar design be established
for a range of tree and food crops over varied ecological sites
in tropical Africa. These will serve as valuable demonstrations
and at the same time yield useful data for afforestation.

From 1977 to 1981 the Institute of Agronomic Research
(lRA), through its Centre for Forestry Research in Edea,
Cameroon, conducted a project with the objectives of: identifying
the c/imatic and ecological factors of Edea (from literature,
meteorological services, and soil analyses); studying the farming
systems and the utilization of forest products in the dense humid
forest zone (through farmer surveys and observations); and
selecting leguminous forest species of agronomic and forestry
interest (through elimination trials). The soil analysis
confirmed that the soil is nutrient-poor. The study of farming
systems showed that, in Edea, the peasant farmers cultivate
0.5-4.2 ha and that collective farming is atypical. Furthermore,
the farming system is essentially a shifting agriculture
involving a fallow of three to seven years. Mixed cropping is
common, and the farming practices involve very simple technology
(cutlasses, hoes, and fire). Land used by the community is often
subject to erosion. Finally, the peasant population thrives
principally on cassava, taro (Colocasia esculenta), macabo
(Xanthosoma sagittifolium), yams, sweet potatoes, bananas, and
plantains. Also planted are maize, groundnuts, and beans. The
forest trees associated with traditional farming systems were
found, as in the case of the humid forest zone of Western Nigeria
(Getabun 1980), to be Leucaena leucocephala, which is planted on
cocoa and coffee farms as a shade tree, and Treculia africana,
Irvingia gabonensis, Dacryodes edulis, Samanea (Pithecolobium)
saman, Cassia siamea, and Pterocarpus soyauxii. Tree elimination
trials led to a preliminary selection (made on the basis of mean
height growth attained after 18 months), in order of descending
importance, of Albizia falcataria, Samanea saman, Albizia
lebbeck, Leucaena leucocephala, and Pterocarpus soyauxii as
suitable for use in subsequent experiments in Edea because of
their potential for yam-supports, shade trees, improvement of
soil, and pulp production - a matter of prime importance to
CELLUCAM, the pulp manufacturing company established in Edea.

Introduction

The importance of agro-forestry research as a tool to improve
agricultural production, and therefore the standard of living of
the people, in the humid tropical zone was brought home to the
research sector (the National Office for Scientific and Technical
Research at the time) in the United Republic of Cameroon in 1976
by the International Development Research Center (IDRC). This
importance was stated to lie in the possibility that research
could formulate agro-forestry systems to replace the shifting
agriculture that is prevalent in many humid tropical zones. In
particular, agro-forestry systems promised that the use of
trees-especially leguminous forest trees- to replace the bush
fallows could ensure the improvement of the soil and, at the same
time, provide forest produce that could yield revenue to the
peasant farmers.

An agro-forestry project was, thus, conceived and agreed upon
by IDRC and the United Republic of Cameroon in 1976. The first
phase of the project was to last three years (i.e., until April
1980), but in fact it did not end until March 1981. This was due,
in large part, to the delay in purchasing the project vehicles.

Objectives

The objectives defined for the project were: to identify the
climatic and ecological factors of Edea, which is located in the
dense humid forest of Littoral Province; to study the farming
systems and the utilization of forest products in this zone; to
select leguminous forest species that would be of agronomic and
silvicultural interest in the zone being studied and to determine
the propagation techniques for such species; and to establish
experimental plantations with the object of studying the effects
of leguminous species on soil impoverished by shifting
cultivation.

Methods

The study of climatic and ecological factors was carried out
partly through a review of existing literature, partly through
contact with the meteorological services at Edea, and partly
through analysis, in the soils laboratory at Ekona, of soil
samples taken from the principal soil types of Mangombe, Edea.
With regard to the latter, six samples of upland, sandy soil (30
cores were bulked to yield a sample) from Mangombe (under forest,
under food crops, and under fallow) were taken and analysed in
the laboratory at Ekona. Again, in May 1978, 15 samples were
taken at different depths under natural secondary forest, food
crops, five-year old fallows, and leguminous forest species
(Afzelia pachyloba, Piptadeniastrum africanum).* The soil studies
of May 1978 were repeated in May 1979 to cover the upland as well
as the other two subtypes of Mangombe, i.e., gravelly and
hydromorphic soils.

The study of farming systems was essentially an exercise in
enumeration. Randomly selected peasant farmers were asked to
address themselves to standard questionnaires on their farming
activities. These data were supplemented by the inspection and
measurement of the farms owned by the farmers. Difficulties were
encountered by the lack of a suitable researcher to undertake a
detailed socio-economic study of Edea and its environs. In the
study of the utilization of forest products in traditional
farming, staff observed and recorded the species of the shade
trees planted in traditional cocoa and coffee farms and the
multipurpose trees found in the permanent compound farms.

The selection of leguminous forest species of interest for
agro-forestry was made in elimination trials that were aimed at
identifying local or exotic species that would thrive in the
ecological conditions of Edea. A search was undertaken for mature
leguminous seed bearers at Edea and at Kumba, while seeds of
exotic leguminous species were acquired from various individuals
and forestry research institutions. The availability of seeds and
problems in germinating certain species severely limited the
scope of the elimination trials.

The first elimination trial was planted in August 1978 and
covered 2 ha. It involved leguminous species from only eight seed
lots; five of the seed lots were planted according to a
statistical design (complete randomized blocks, five treatments,
four replications) at a spacing of 4 x 4 m in plots measuring 40
x 25 m (66-70 plants/plot). The remaining three seed lots,
because of seed shortage, were simply planted in unreplicated
plots. The seed lots planted in the 1978 trial were: Pterocarpus
soyauxii, P. osun, Afzelia pachyloba, Acacia sp., Tetrapleura
tetraptera, and three lots of Leucaena leucocephala.

The 1979 elimination trial involved 23 seed lots that were
sown between February and April 1979 and planted out in July
1979. The plantings were made in an area slightly less than 2 ha.
As a result of the low germination rates for many of the seed
lots, planting was not carried out according to a strict
statistical design. Still the principle of replication was
maintained, with 23 plots in each block corresponding to the
different seed lots. The spacing was 3 x 2 m, but, as a
consequence of the limited planting material, two sizes were
adopted for unit plots: small plots (each measuring 36 m²) and
large plots (each measuring 72 m²). There were 21 plants per
large plot, whereas the number of plants in each small plot
ranged from one to nine. The 23 seed lots included one of the
seed lots (Tetrapleura tetraptera) employed in the 1978 trials.

The site preparation for both the 1978 and 1979 trials
consisted of felling the big trees, clearing the underbrush,
burning, staking, and hole digging. The planting stock for the
1978 trial consisted of striplings, wildings, and stumps. For the
1979 trial, however, only seedlings raised in polythene pots were
used.

Results

Climatic and Ecological Factors

Mangombe (in Edea) is at latitude 4°00'N and longitude
10°15'E. Its altitude is 32 m above sea level. The mean annual
rainfall is 2,600 mm. The rainfall distribution is generally
regular, there being some rainfall even in the dry season
(November-April). The temperatures are high; the mean monthly
maximum and minimum temperatures were 27.8°C and 23.2°C,
respectively, in 1978.

According to a study carried out by CTFT (1969), there are
three distinct soil types in Mangombe:

Sandy solis, situated on the uplands, which are deep,
stone-free and suitable for plantations; these soils
cover about 60 per cent of the area;

Gravelly soils, situated on the slopes, with lateritic
gravel or quartz or altered rock (mica schist or gneiss);
these are unsuitable for plantations and cover about 30
per cent of the area; and

Hydromorphic soils, situated on valley bottoms, often
gravelly, frequently moisture-laden in the vicinity of
water courses; these soils are also unsuitable for
plantations and cover about 10 per cent of the area. The
field work carried out by our forestry research centre
confirmed these results.

Laboratory analysis showed that the upland (sandy) soils were
acidic (pH 4) and varied little between the two depths 1020 cm,
40-60 cm). In general the physical properties were quite good.
Soil water was well distributed except during heavy rainfall;
clay particles were 35 40 per cent under forest, 45 per cent
under food crops, and 37-40 per cent under fallow. There was a
good distribution of the fine and heavy particles, and stones
were absent.

Soil chemical properties were poor, probably because of heavy
leaching. According to the 1977 analysis total nitrogen showed a
tendency to increase with depth, from 0.09-0.14 per cent and
0.09-0.13 per cent, respectively, for soils under forest and
under food crops. The sum of exchangeable bases was, on the
whole, low, as was available phosphorus. In the 1978 study the
content of organic matter decreased with depth-in sharp contrast
to the trend exhibited in the 1977 samples. Nitrogen also
decreased with depth in the 1978 samples (i.e., from 0.1 per cent
at the surface to 0.06 per cent at 110 cm depth). The contrasting
results on organic matter and nitrogen levels in 1977 as compared
with 1978 are confusing unless the 1977 result is erroneous. This
possibility is supported by results from the May 1979 samples.

Soils under leguminous forest species (Afzelia pachyloba and
Piptadeniastrum africanum) exhibited slightly higher amounts of
organic matter (1.51-1.22 per cent at 0-40 cm) than was found in
soils under forest, food crops, and fallow.

Farming Systems

The farmers in and around Edea have holdings of about 0.54.2
ha. Farming on a collective basis is rather rare, although there
is one example, the Groupe des Agriculteurs Modernes supported by
FONADER (Fonds National de Developpement Rural; often referred to
as the farmers' bank).

The farming system is essentially a shifting agriculture
involving a fallow period of three to seven years. Mixed cropping
is common, and the cultural practices of field preparation are
partial or complete clearing and burning, making such land
subject to erosion.

The peasant population depends principally on cassava, taro
(Co/ocasia esculenta), macabo (Xanthosoma sagittifolium), yams,
sweet potatoes, bananas, and plantains. Maize, groundnuts, and
beans are also planted. The two principal industrial crops of
Littoral Province are robusta coffee and cocoa. The
Sanaga-Maritime Division (Edea) is third among the divisions of
Littoral Province for the production of both coffee and cocoa.
Rubber and oil palms are also found as industrial crops in
Sanaga-Maritime Division.

The forest trees associated with traditional farming systems
were found, as in the case of the humid forest zone of western
Nigeria (Getahun 1980), to be Leucaena leucocephala, which is
planted in cocoa and coffee farms as a shade tree, and Treculia
africana, Irvingia gabonensis, Dacryodes edulis, Samanea saman,
Cassia siamea, and Pterocarpus soyeuxii, which are multipurpose
trees present in permanent compound farms.

Selection of Leguminous Forest Species

Mean height was the only measurement taken after 18 months in
the elimination trials. No statistical analysis was undertaken to
determine whether or not the difference between the mean heights
for any selected pair of seed lots was significant. Nevertheless,
the results (table 1) seemed to justify some conclusions:

Albizia falcataria (which recorded 9.1 m) grew
significantly faster than any of the other species, with
the next species in height performance (Samanea saman)
attaining only 5.5 m;

There seems to have been little difference among the
Leucaena leucocephala provenances from Hawaii; they
showed a height growth ranging from 4.2 m (for K132) to
4.4 m (for K6); and

From the work carried out by the agro-forestry project, it
seems that the leguminous species Albizia falcataria, Samanea
saman, A. Iebbeck, Leucaena leucocephala, and Pterocarpus
soyauxi; should be provisionally selected as trees that will
thrive in the humid zone of Edea. It is immensely important to
the future of the agro-forestry research project in Edea that the
majority of the species selected from our elimination trials were
found to exhibit a great natural capacity for nodulation. L.
Ieucocephala is the only species likely to be used in our future
work that did not appear to nodulate in our experiment either in
the nursery or in the field. These aspects are worthly of further
investigation. Given the potential of these selected leguminous
species for soil improvement, use as shade trees, and pulp
production, they should be given first consideration in the
choice of species to be used for the establishment of
experimental plantations.

In view of the great role that is likely to be played by
CELLUCAM in the socio-economic development of Edea in the near
future, the choice of species to be used for the establishment of
the experimental planations should also include pulp species
(e.g., Pinus caribaea, Eucalyptus urophylla, Gmelina arborea)
which have been chosen for use in the next five-year
reforestation programme of CELLUCAM.

The specific objectives for the experimental plantations
should include:

Study of the effect of tree plantations on the
restoration of soil fertility in soils depleted by
farming;

Study of the effect of spacing on the production of wood
and food crops; and

A preliminary inventory of the tree-insect/fungus/ virus
associations so that tree species which act as hosts to
the pests of agricultural crops in the Edea region can be
identified.

Acknowledgement

Immense thanks are due Patrick Shiembo, the agro-forestry
research assistant at Edea, for kindly accepting to carry out the
final measurements of the 1979 elimination trial.

TABLE 1. List of Seedlots Sown in 1979: Their Germination,
and Height (m) at 18 Months